Control circuit for an air conditioning system

ABSTRACT

An air conditioning system is provided to supply treated air to an area. The system includes a refrigeration unit comprising a motor-driven compressor, a condenser, an evaporator, and expansion means. The motor includes a run winding and a start winding connected in parallel. The start winding has a positive temperature coefficient thermistor connected in series therewith to interrupt operation of the start winding after the motor has reached its operating speed. A bimetallic switch responsive to the temperature of the thermistor is actuated thereby. During normal operation, a bypass circuit about the bimetallic switch prevents the switch from having any effect on the operation of the compressor motor. When the compressor motor is deenergized, the bypass becomes ineffective. The switch, which has been opened by the temperature of the thermistor, prevents reenergization of the compressor motor until a predetermined period of time has elapsed.

United States Patent 3,695,054 Barry Oct. 3, 1972 [54] CONTROL CIRCUITFOR AN AIR Primary Examiner-William E. ODea CONDITIONING SYSTEMAssistant Examiner-P. D Ferguson [72] Inventor: Vincent T. Barry,Camillus, N.Y. gg fl Mamn and Raymond Cur- [73] Assignee: CarrierCorporation, Syracuse, NY. [22] Filed: May 25, 1971 [57] ABS CT An airconditioning system is provided to supply [21] Appl 146719 treated airto an area. The system includes a refrigeration unit comprising amotor-driven compressor, a 52 US. Cl. ..62/1 15, 62/158, 62/228,condenser, an evaporator, and expansion means- The 313/221 H, 318/473motor includes a run winding and a start winding con- 51 int. Cl ..F25b1/00, G05b 5/00 nected in p l T start winding has a positive 53 Field fs g 5g 22 1 5; 313 22 15 temperature coefficient thermistor connected inseries 31 /22 H, 229 47 472 473 therewith to interrupt operation of thestart winding after the motor has reached its operating speed. A [56]References Cited bimetallic switch responsive to the temperature of thethermistor is actuated thereby. During normal opera- UNITED STATESPATENTS tion, a bypass circuit about the bimetallic switch prevents theswitch from having any effect on the a operation of the compressormotor. When the coma 4 X pressor motor is deenergized, the bypassbecomes in- Ve1nott....l. X effective. The Switch, has been opened the2403156 7/1946 Spear et a l22 temperature of the thermistor, preventsreenergization 5 33 2% i of the compressor motor until a predeterminedperiod p In h ela 3,559,420 2/l971 Lipscomb ..318/472 x 0 as PS8 10Claims, 3 Drawing Figures PATENTE'Ducr 3 m2 SHEET 1 OF 2 INVENTOR.'VINCENT T; BARRY BY 7 ATTORNEY P A T ENTED 3 I973 sum 2 or 2 INVENTOR.

VINCENT T. BARRY BY v FIG. 3

ATTORNEY CONTROL CIRCUIT FOR AN AIR CONDITIONING SYSTEM BACKGROUND OFTHE INVENTION The utilization of split-phase induction motors to drivethe compressors of refrigeration units has become increasinglyprevalent. Such a refrigeration unit, including the compressor,condenser, evaporator, and expansion means, is typically employed in anair conditioning system, such as a room air conditioner.

A split-phase motor is a single-phase induction motor equipped with anauxiliary winding displaced in magnetic position from, and connected inparallel with, the main winding. When the motor has attained apredetermined speed, the circuit to the auxiliary winding is opened. Themeans to open the auxiliary circuit have generally included mechanicallyoperated devices, such as centrifugal switches. However, it has beenproposed that a temperature sensitive resistance element, such as apositive temperature coefiicient thermistor, be used in series with theauxiliary winding. The self-heating effect of the thermistor operates tointerrupt substantially all flow of current to the auxiliary winding toeffectively remove same from operation once starting of the compressormotor has been obtained.

The utilization of split-phase motors is limited toapplications wherelow starting torque is required. In the conventional air conditioningsystem refrigeration unit, when the electrical circuit to the compressormotor is opened for any reason, as for example, by opening a safetyswitch responsive to an abnormal load condition in the system, thecircuit is completed again immediately upon the closing of the safetyswitch. In addition, rapid cycling of the thermal actuated controlswitch or conventional thermostat responsive to room temperature, willinterrupt the operation of the compressor motor and then rapidly restartsame.

Under such conditions, refrigerant pressure in the system may not havehad sufficient time to equalize; therefore, when the circuit is closed,the split-phase motor will be unable to start the compressor. Typically,overload mechanisms are provided with the motor to interrupt the supplyof current thereto, to prevent surge or locked rotor current fromflowing to the motor for too long a period of time if the motor shouldfail to start.

The object of this invention is to provide a novel control circuit forair conditioning systems of the type discussed above, operable toprevent the compressor motor from being restarted for a predeterminedperiod of time after operation thereof has been interrupted. The novelcontrol is particularly suitable for use with split-phase motors of thetype having a thermistor in series with the auxiliary or start winding.

SUMMARY OF THE INVENTION This invention relates to an air conditioningsystem including a refrigeration unit having a motor driven compressor,a condenser, an evaporator and expansion means. The motor for drivingthe compressor is of the type known as a split-phase motor.

In series with the auxiliary or start winding of the split-phase motoris a positive temperature coefficient thermistor or other temperatureresponsive resistance element, having the characteristics that theresistance thereof will increase as a function of the temperature.

Upon startup of the compressor motor, the resistance of the seriesconnected resistance element is low so substantially all of the startingcurrent is supplied to the auxiliary and run windings. Once the motorhas attained its predetermined speed, the resistance of the element willhave risen to a level so that substantially all flow of current to theauxiliary winding is interrupted; only the run winding will remain inthe circuit.

When operation of the refrigeration unit is stopped, the refrigerantpressure between the high and low sides of the system will be at asubstantial differential. To prevent the restarting of the compressormotor for a predetermined period of time, was to allow the pressuredifierential to substantially equalize, the control circuit regulatingthe operation of the compressor motor includes switch means responsiveto the temperature of the resistance element connected in series withthe start winding.

When the temperature of the resistance element has increased due to theflow of the current therethrough, the temperature responsive switch willopen. However, during the normal operation of the compressor, theopening of such switch will have no effect thereon. Once the operationof the compressor motor has been interrupted, restarting of thecompressor motor will be prevented so long as the switch remains open.The switch will close after a predetermined period of time has elapsedduring which time the temperature of the thermistor and switchresponsive thereto will return to a normal level.

The specific details of the invention and their mode or function will bemade most manifest and particularly pointed out in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a typeof air conditioning system including a refrigeration'unit illustratingthe present invention;

FIG. 2 is an enlarged detailed schematic wiring diagram of a portion ofthe air conditioning system illustrated in FIG. 1, showing a preferredform of control in accordance with my invention; and

FIG. 3 is a fragmentary schematic diagram of an alternative embodimentof my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, and inparticular to FIG. 1, there is schematically shown an air conditioningsystem employing a refrigeration unit incorporating a control inaccordance with my invention. The refrigeration unit is representativeof a type utilized in window mounted room air conditioners.

An outdoor heat exchange coil or condenser 10 is connected by means ofline 11 with the discharge side of a suitable refrigerant compressionmechanism, for example, a reciprocating type compressor 12. The gaseousrefrigerant produced in compressor 12 flows to condenser 10 and iscondensed by ambient air routed over the surface of the condenser byoutdoor fan 13. Liquid refrigerant formed in condenser 10 flows via line14, thermal expansion valve 15, and line 16 to evaporator 17. It isunderstood other suitable expansion devices such as a capillary tube,may be employed in place of expansion valve 15.

Liquid refrigerant in evaporator 17 is converted to vaporous refrigerantas it extracts heat from the medium, for example, air passed over itssurface by fan 18. The cool air is discharged into the area beingconditioned through a suitable outlet (not shown). Vaporous refrigerantfrom evaporator 17 flows via suction line' 19 to compressor 12 tocomplete the refrigerant flow cycle.

Again referring to FIG. 1, a preferred form of the control circuit forthe air conditioning system refrigeration unit hereinabove described isschematically shown. A suitable source of electric power, represented bylines L and L is connected to primary winding 24 of transformer 23. Itis understood a poly-phase source of electric power may be employed ifthe circuit is suitably modified.

The secondary winding 25 of transformer 23 is connected to switch 26,responsive to the temperature of air circulating in the area beingserved by the equipment. When thermally actuated switch 26 is closed,current is supplied to control relay 27. Energization of control relay27 closes normally open switches 29 and 30. Once switch 29 has beenclosed, fan motors and 21 are energized thereby actuating fans 13 and18. The closure of switch 30 supplies current through normally closedswitches 31, 32 and 33 to compressor contactor coil 35. Device 34, to bemore fully explained hereinafter, is connected in series with switches31, 32 and 33 and coil 35. Energization of compressor contactor coil 35closes normally open switch 36. The closure of normally open switch 36connects motor 22 across lines L and L thereby starting compressor 12.The energization of compressor contactor coil 35 also closes normallyopen switch 37 for a reason to be more fully explained hereinafter.

Normally closed switches 31, 32 and 33 are safety devices; respectivelya high-pressure cutout, a lowpressure cutout, and a motor overloadcutout. Other safety devices known to the art, such as a low oilpressure cutout, may also be used. The occurrence of the conditionprotected against will open the particular switch, thereby eitherpreventing the compressor motor from starting or stopping the compressormotor during the normal operation of the system.

Referring now to FIG. 2, there is shown an enlarged detailed view of aportion of the control circuit shown in FIG. 1, illustrating the detailsof my invention.

Motor 22 is of the type known to those skilled in the art as asplit-phase motor. The split-phase motor includes parallel connectedwindings 40 and 41, respectively the main and auxiliary or startwindings. Connected in series with auxiliary winding 41 is temperaturesensitive resistance element 42, shown as a positive temperaturecoefiicient thermistor. As is known to those skilled in the art, thepositive temperature coefficient thermistor has a characteristic suchthat its resistance increases as a function of its temperature. Inseries with compressor contactor coil 35 is device 34. Device 34includes normally closed switch 43, con- I nected to bimetallic element44. Bimetallic element 44 is responsive to the temperature of thermistor42. As the temperature of thermistor 42 increases due to the flow ofcurrent therethrough, bimetallic element 44 warps to open switch 43, asrepresented by the solid lines of FIG. 2.

With switch 43 in its normally closed position, as represented by thedotted lines of FIG. 2, energization of coil 35 will occur upon theclosure of switch 30. Switch 36 will close to provide current to thewindings of motor 22. As noted hereinbefore, as the current flows toauxiliary winding 41 through thermistor 42, the current operates toincrease the temperature and thus the resistance thereof. When the motorhas attained its predetermined speed, winding 41 is effectively disabledby the substantial resistance presented to current flow thereto bythermistor 42.

The energization of contactor coil 35 closes normally open switch 37.Switch 37 provides a shunt or bypass about switch 43. Since switch 37closes before switch 43 opens, the opening of switch 43 during normalrunning conditions of the compressor motor does not have any effectthereon.

When the operation of the compressor motor is interrupted, for example,by the opening of any one of the switches 31, 32 or 33, or by theopening of thermal responsive switch 26, the flow of current to coil 35is interrupted, thereby opening switches 36 and 37.

When switch 36 opens, the flow of current to the compressor motor isinterrupted. However, the increased temperature of the thermistor and ofthe bimetallic element 44 which is responsive thereto; has not beendissipated; switch 43 is still in its open position.

Assume the particular switch that has opened to interrupt the flow ofcurrent to compressor motor 22 subsequently recloses. With switch 43still in its solid line position, in response to the temperature ofbimetallic element 44, the flow of current to coil 35 is prevented.

If the compressor motor were to be permitted to restart immediatelyafter it has been deenergized, the refrigerant pressure in the systemwould be at a substantially high differential. The compressor motor,since it is a split-phase type, would not have sufficient torque torestart the compressor. The locked rotor current caused to flow to thewindings would deteriorate and in serious cases, completely burn themout.

By maintaining switch 43 in an open position for a substantiallypredetermined period of time, as determined by the time required forthermistor 42 and thus bimetallic element 44 to dissipate their heat tothe ambient air, the pressure differential of the refrigeration unitwill substantially equalize. Thus, when switch 43 is returned to itsdotted line, or closed position, the pressure difierential will besubstantially equalized, and compressor motor 22 will have sufficienttorque to start the compressor motor without introducing the problemshereinabove described.

Referring now to FIG. 3, an alternative embodiment of my invention isdisclosed. In lieu of device 34, a second temperature responsiveresistance element, such as a positive temperature coefficientthermistor 45 is placed in series with coil 35. Similar to device 34,thermistor 45 is responsive to the temperature of thermistor 42.

Upon the initial starting of compressor motor 22, the resistance ofthermistor 45 is at a low level, so electrical energy is suppliedtherethrough to energize coil 35, to thereby close switches 36 and 37.As the temperature of thermistor 42 increases due to the flow of currenttherethrough, a concurrent increase occurs in the resistance ofthermistor 45. The increased resistance of thermistor 45 is caused bythe flow of current therethrough and the increased temperature ofthermistor 42. I

Although the passage of electrical energy-through thermistor 45 issubstantially interrupted, compressor motor 22 continues to operate-dueto the prior closure of switch 37. In all other respects, the operationof the embodiment shown in FIG. 3, is the same as heretofore describedfor the embodiment shown in FIG. 2.

A further benefit is obtained by employing a control circuit inaccordance with my invention. As noted before, switch 29 will close uponthe energization of relay 27 in response to the closure of switch 26.When switch 29 closes, fans 13 and 18 will be actuated. By actuating thefans, even if the compressor cannot be immediately restarted, due toswitch 43 being in an open position, the flow of air over the condenserand evaporator caused thereby, will reduce the time required for thepressure differential to substantially equalize. This will insure theavailability of sufficient torque to restart compressor motor 22 onceswitch 43 has closed due to the cooling of thermistor 42.

In addition, by maintaining the compressor deenergized for thesubstantially predetermined period of time so as to allow thetemperature and resistance of the thermistor to return to its normallevel, current flow to the start winding upon reenergization will beinsured.

While I have described and illustrated apreferred embodiment of myinvention, my invention should not be limited thereto but maybeotherwise embodied within the scope of the following claims.

lclaim:

1. In an air conditioning system operable to supply treated air to anarea including a refrigeration unit comprising a compressor, acondenser, an evaporator and expansion means connected in a closedcircuit, a motor for actuating said compressor, said motor having a runwinding and a start winding connected in parallel, the improvement whichcomprises a control circuit to regulate the operation of saidrefrigeration unit comprising:

A. a supply circuit for providing electrical energy to said compressormotor, including thermally responsive means operable to energize saidsupply circuit in response to temperature conditions in said area;

B. a temperature responsive resistance element connected in series withsaid start winding of said compressor motor, the resistance of saidresponsive means substantially increasing as a function of its owntemperature, the temperature thereof being increased by the How ofstarting current therethrough; and

C. heat sensitive means responsive to the temperature of said resistanceelement, an increase in the temperature of said resistance elementplacing said heat sensitive means in a state such that flow ofelectrical energy therethrough is substantially interrupted, said meanswhen in said state serving to prevent restarting of said compressormotor when the supply of electrical energy thereto has beendiscontinued, restarting of said compressor motor being prevented untilthe temperature of pressor motor, said bypass means becoming inoperablewhen the supply of electrical energy to said compressor motor has beeninterrupted.

4. The combination in accordance with claim 3 further including:

A. means operable to supply a medium in heat transfer relation with saidcondenser; and

B. means operable in response to said thermally responsive switch toactuate said medium supply means, irrespective of the energization ofsaid compressor motor.

5. The combination in accordance with claim 1 further including:

A. means operable to supply a medium in heat transfer relation with saidcondenser; and

B. means operable in response to said thermally responsive switch toactuate said medium supply means, irrespective of the energization ofsaid compressor motor.

6. The combination in accordance with claim 1 wherein said heatsensitive means includes a second temperature responsive resistanceelement.

7. The combination in accordance with claim 6 wherein said controlcircuit further includes bypass means about said second resistanceelement to render said element inoperable during the operation of saidcompressor motor, said bypass means becoming inoperable when the supplyof electrical energy to said compressor motor has been interrupted.

8. The combination in accordance with claim 7 further including:

A. means operable to supply a medium in heat transfer relation with saidcondenser; and

B. means operable in response to said thermally responsive switch toactuate said medium supply means, irrespective of the energization ofsaid compressor motor.

- 9. The method of operating an air conditioning system including arefrigeration unit, having a compressor, a condenser, an evaporator andexpansion means connected in a closed circuit, a motor for actuating thecompressor including an auxiliary winding connected in parallel with amain winding, a temperature responsive resistance element beingconnected in series with the auxiliary winding, comprising the steps of:

A. supplying electrical energy through a device to energize theauxiliary and main windings of the motor to start the motor to actuatethe compressor;

B. increasing the temperature and the resistance of the resistanceelement in series with the auxiliary winding to discontinue theoperation 'of the auxiliary winding;

compressor beingprevented until the device is placed in a state wherebythe flow of electrical 'energy therethrough may recommence, thereenergization of the compressor being thus prevented for substantiallya predetermined period of time.

10. The method in accordance with claim 9 further including:

supplying a medium in heat transfer relation with said condenser, thesupplying of said medium being independent of the operation of saidcompressor motor.

1. In an air conditioning system operable to supply treated air to anarea including a refrigeration unit comprising a compressor, acondenser, an evaporator and expansion means connected in a closedcircuit, a motor for actuating said compressor, said motor having a runwinding and a start winding connected in parallel, the improvement whichcomprises a control circuit to regulate the operation of saidrefrigeration unit comprising: A. a supply circuit for providingelectrical energy to said compressor motor, including thermallyresponsive means operable to energize said supply circuit in response totemperature conditions in said area; B. a temperature responsiveresistance element connected in series with said start winding of saidcompressor motor, the resistance of said responsive means substantiallyincreasing as a function of its own temperature, the temperature thereofbeing increased by the flow of starting current therethrough; and C.heat sensitive means responsive to the temperature of said resistanceelement, an increase in the temperature of said resistance elementplacing said heat sensitive means in a state such that flow ofelectrical energy therethrough is substantially interrupted, said meanswhen in said state serving to prevent restarting of said compressormotor when the supply of electrical energy thereto has beendiscontinued, restarting of said compressor motor being prevented untilthe temperature of said resistance element has decreased to its normallevel, said heat sensitive means being thereby placed in a state suchthat electrical energy is passed therethrough.
 2. The combination inaccordance with claim 1 wherein said heat sensitive means includes abimetallic element; and a switch means operably connected thereto. 3.The combination in accordance with claim 2 wherein said control circuitfurther includes bypass means about said switch means to render saidswitch means inoperable during the operation of said compressor motor,said bypass means becoming inoperable when the supply of electricalenergy to said compressor motor has been interrupted.
 4. The combinationin accordance with claim 3 further including: A. means operable tosupply a medium in heat transfer relation with said condenser; and B.means operable in response to said thermally responsive switch toactuate said medium supply means, irrespective of the energization ofsaid compressor motor.
 5. The combination in accordance with claim 1further including: A. means operable to supply a medium in heat transferrelation with said condenser; and B. means operable in response to saidthermally responsive switch to actuate said medium supply means,irrespective of the energization of said compressor motor.
 6. Thecombination in accordance with claim 1 wherein said heat sensitive meansincludes a second temperature responsive resistance element.
 7. Thecombination in accordance with claim 6 wherein said control circuitfurther includes bypass means about said second resistance element torender said element inoperable during the operation of said compressormotor, said bypass means becoming inoperable when the supply ofelectrical energy to said compressor motor has been interrupted.
 8. Thecombination in accordance with claim 7 further including: A. meansoperable to supply a medium in heat transfer relation with saidcondenser; and B. means operable in response to said thermallyresponsive switch to actuate said medium suppLy means, irrespective ofthe energization of said compressor motor.
 9. The method of operating anair conditioning system including a refrigeration unit, having acompressor, a condenser, an evaporator and expansion means connected ina closed circuit, a motor for actuating the compressor including anauxiliary winding connected in parallel with a main winding, atemperature responsive resistance element being connected in series withthe auxiliary winding, comprising the steps of: A. supplying electricalenergy through a device to energize the auxiliary and main windings ofthe motor to start the motor to actuate the compressor; B. increasingthe temperature and the resistance of the resistance element in serieswith the auxiliary winding to discontinue the operation of the auxiliarywinding; C. sensing the increased temperature of the resistance elementupon the passage of electrical energy therethrough to place the devicein a state whereby the flow of electrical energy therethrough issubstantially interrupted in response to the increased temperature ofthe resistance element; D. interrupting the passage of electrical energyto the main winding to deenergize the compressor motor; and E.maintaining the device in its state whereby the flow of electricalenergy is interrupted until the temperature of the resistance elementhas decreased to its normal level, reenergization of the compressorbeing prevented until the device is placed in a state whereby the flowof electrical energy therethrough may recommence, the reenergization ofthe compressor being thus prevented for substantially a predeterminedperiod of time.
 10. The method in accordance with claim 9 furtherincluding: supplying a medium in heat transfer relation with saidcondenser, the supplying of said medium being independent of theoperation of said compressor motor.